Glioblastomas rank among the most lethal of all human cancers. Current therapy includes maximal surgical resection, followed by combined radiotherapy and oral chemotherapy (temozolomide), and adjuvant temozolomide. Maximal current therapy offers only palliation. Median survival for glioblastoma patients has been reported to be 15-21 months, but these data are derived from patients with favorable age and performance status. Recurrent glioblastoma therapy is limited with little evidence for effective therapy. Treatment failure is derived from numerous causes, including the presence of stem-like tumor cells, called glioblastoma stem cells (GSCs). GSCs contribute to radioresistance, chemoresistance, invasion, immune escape, and angiogenesis. GSCs display dependencies on specific signal transduction pathways and epigenetic regulation, associated with metabolic reprogramming. Almost all living organisms on earth are exposed to a regular 24-hour day-night cycles generated by planet?s rotation around its own axis, which in return leads to the evolution of intrinsic, entrainable circadian rhythm driven by cell autonomous biological clocks. Molecular oscillation of transcriptional circuitry to regulate circadian rhythms include positive regulation by the BMAL1 and CLOCK transcription factors, with two negative regulatory loops that either transcriptionally downregulate BMAL1 or bind and inhibit BMAL1:CLOCK transcriptional complexes. In our proposed studies, we leverage preliminary findings that the circadian rhythm machinery serves distinct cellular and molecular roles in maintenance of GSCs. We will determine the necessity for circadian rhythm regulation in GSCs mediate through metabolic reprogramming and selective activation of oncogenic pathways. To translate these efforts into novel clinical paradigms, we are using a novel class of agents that target circadian clock function. These small molecule inhibitors are brain penetrant and can be combined with other therapies to create synergistic targeting of GSCs. To generate the most effective therapeutic paradigm, we will interrogate the preclinical utility of novel targeted therapies that disrupt the circadian rhythm oscillatory loop that could accentuate the efficacy of conventional therapy. Collectively, the proposed studies will lay the foundation for improved understanding of circadian rhythm regulation in cancer stem cell biology with possible application to improved oncologic care.